58 



TIIK MUSCLES. 



neath the eye ; and are inserted externally by means of tendinous 

 fibres into the superior border of the upper jaw. 



9. From the foregoing muscle certain fibres pass to the lower 

 eyelid, which may be regarded as a depressor palpebrae infer! oris 

 (Fig. 52 d.p\ 



Maiiz 1 has described a muscle as depressor palpebrae infer loris 

 which arises in the neighbourhood of the external angle of the 

 eye, somewhat behind and below the lower border of the orbit, thence 

 passes obliquely upwards to be inserted into the lower eyelid. This 

 description is right as regards the insertion, but needs correction 

 as regards the orig-in. The muscle is attached to the orbital border 

 in so far that the tendinous expansion, into which the levator lulbi 

 passes at its external border, is attached into the upper jaw ; this 

 bundle splits off from the upper surface of the levator lulbi at its 

 middle, and runs outwards on the under surface of the eyeball to the 

 hinder part of the lower eyelid. 



10. Tendon of the inonbrana uictilans* (Fig. 53 ?/). The 

 pigmented free border of the nictitating membrane passes, at the 



inner and outer angles of the eye, into a ten- 

 don which passes for some distance through 

 fibrous tissue, then descends to the under 

 surface of the eyeball and joins that of the 

 opposite side, so that the free border of the 

 eyelid, together with this tendon, form a com- 

 plete ring. The tendinous part of the ring, 

 which is thin and thread-like, is found 

 on the under surface of the eyeball, and lies 

 under the m. retractor lulbi, and is bound to 

 this muscle by connective tissue. Manz is 

 right in saying that the two muscles described 

 by Duges as levatores palpebrae inferiores (or- 

 ' Tendon of membrana nic- bito-palpebral anterieur and posterieur, n. 5 

 r M. retractor buiw, lower and 6) do not exist ; as is also the suggestion 



r' Second part of same. that he haS COnfoUllded the tendon of the 



nictitating membrane with these; this is 

 clearly shown in the figure in Plate VI of Duges. With regard 

 to the actions of these eye-muscles, it is plain that the four straight 



1 Manz, Berichte der naturf. Gesellschaft zu Freiburg, 2 Band, 4 Heft, 1862, 

 P- 39'- 



a Compare Manz, I. c. 



\J 



Eye-musoles of Rana cscu- 

 lenta, from below, the m. 

 recti and obliqui have 

 been removed. 



